Reformating reactions for materials such as methane may be carried in a dry reforming process or a steam reforming process and may use a fixed bed or a fluidized bed. Steam reforming of methane is a process in which methane is brought into contact with steam at high temperature (1100 K) and pressure (3000 kPa) over a catalyst. The result is the production of a mixture of CO, CO2 and H2, commonly referred to as synthesis gas or syngas. Steam reforming of methane is the major source of synthesis gas for the production of chemicals such as methanol and ammonia and is the primary source of syngas for hydrogen production. On the industrial scale, steam reforming of methane is carried out in fixed bed reactors using a catalyst composed of nickel dispersed on a monolithic support such as α-alumina or magnesia see for example C. N., Satterfield, Heterogeneous Catalysis in Industrial Practice, McGraw Hill, Inc. New York, 1991. Steam to methane ratios in excess of 3:1 are used in order to promote high conversions of methane and limit the production of coke.
Recently, the use of reactors that combine hydrogen permeable membranes with fluidized beds for the steam reforming of methane has been growing. In light of this, a new process concept has been developed at the Chemical Reactor Engineering Centre located at the University of Western Ontario (CREC-UWO). This process called (Catforming, combines composite palladium/inconel hydrogen permeation membranes with steam reforming carried out in a circulating fluidized bed reactor (see K., Jarosch, Novel Inconel Supported Palladium Membranes For Hydrogen Separation:. Development, Modeling, and Implication For The CATFORMING Process, M.E.Sc. Thesis, University of Western Ontario, London, Ontario, 1995; T., El Solh, Heterogeneous Catalyst for Methane Reforming, M.E.Sc. Thesis, University of Western Ontario, London, Ontario, 1998: K., Jarosch, Steam Reforming of Methane in a Fast Fluidized Membrane Reactor, Ph.D. Thesis, University of Western Ontario, London, Ontario, 2000: and K., Jarosch, H. I., de Lasa, “Novel Riser Simulator for Methane Reforming using High Temperature Membranes”, Chem. Eng. Sci., vol54, pg. 1455, 1999. U.S. Pat. No. 5,326,550 issued Jul. 5, 1994 to All-Eldin et al. describes a similar process.
In the Catformer process, the reactant gases, steam and methane, are brought into contact with a fluidizable catalyst and the resultant gas-solid suspension is allowed to flow down a reactor tube(s). As the suspension flows down the tube(s), the reforming and water-gas shift reactions take place. Some portion of the tube is to be made of Inconel supported palladium hydrogen permeation membrane allowing the hydrogen to permeate from the reaction zone (see the Jarosch references referred to in the preceding paragraph). After the suspension leaves the reaction zone the catalyst is separated from the product synthesis and the catalyst recirculated to the reactor. Removal of the hydrogen is considered beneficial as follows: a) it allows increased syngas conversion above equilibrium values (supra-equilibrium syngas conversion), b) its favorably affects selectivity (H2/CO ratio), c) it produces pure hydrogen in the membrane permeate side.
Although the Catformer is to be operated at thermodynamic equilibrium, under conditions unfavorable to carbon formation (coke), coke will be generated by kinetic processes. Therefore, the catalyst or some fraction of the catalyst will require periodic regeneration. The regeneration stage, involving coke combustion, will also oxidize the metallic component of the catalyst. It is thus, expected that in the Catforming or parent processes, the fluidizable catalyst will evolve through steps involving coking, regeneration, and reduction. As a result a suitable fluidizable catalyst will have to stand the sequential oxidation and reduction cycles.
A reforming catalyst typically consists of two primary components, the catalyst itself (a metal in the reduced state) and the appropriate catalyst support over which the active metal can be dispersed. The metals in group VIII are active for reforming as are the noble metals. However, economic considerations preclude the use of the noble metals and of the group VIII metals, only Ni has the suitable resistance to oxidation see J. R., Rostrup-Nielsen, Catalysis Science and Technology, vol5, Anderson, J., Boudart, M. (eds.), Springer-Verlag, 1984. The catalyst support is an important catalyst design parameter. Supports have to be mechanically strong, stable under steam atmospheres, high temperatures (750-850° C.) and resistant to metal-support interactions. E., Kuijpers, J., Jansen, A. J., van Dillen, J. W., Geus, “The Reversible Decomposition of Methane on a Ni/SiO2 Catalyst”, Journal of Catalysis, vol72, pg. 75, 1981 and M., Verhaak, A., van Dillen, J., Geus, “Measuring the Acid-Base Properties of Supported Nickel Catalysts Using Temperature-Programmed Desorption of Ammonia”, Applied Catalysis A: General, vol105, pg. 251, 1993 have reported the use of silica (SiO2) as a support. However, the inclusion of silica is generally avoided as it can be volatilized under reforming conditions see the J. R., Rostrup-Nielsen paper referred to above F., Arena, B., Horrell, D., Cocke, A., Parmaliana, N., Giordano, “Magnesia-Supported Nickel Catalysts: I. Factors affecting the structure and Morphological Properties”, Journal of Catalysis, vol132, pg. 58, 1991 and A., Parmaliana, F., Arena, F., Frusteri, S., Coluccia, L., Marchese, G., Martra, A., Chuvilin, “Magnesia-Supported Nickel Catalysts: II. Surface Properties and Reactivity in Methane Steam Reforming”, Journal of Catalysis, vol141, pg. 34, 1993 reported on their investigations of the use of magnesia (MgO) as a catalyst. Even though this type of catalyst was found to be both active and stable, magnesia showed an important drawback: as calcination temperature increased, the amount of available nickel was reduced. This was attributed to the presence of free magnesia in the support which, when hydrated, formed a non-reducible NiO—MgO solid phase.
Given all these facts, α-alumina, formed by the decomposition of hydrated alumina is a preferred support as it is mechanically strong at 1200° C., as required by the conditions of methane reforming (see T., Tsuchida, “Preparation of high surface area (α-Al2O3 and its surface properties”, Applied Catalysis, A, vol105, pg. 141, 1993).
Faujasites have been shown to be effective in several catalytic applications. The basic building block of the faujasite is a truncated octahedron that is connected at four of the hexagonal faces by hexagonal prismatic structures of AlO−4 and SiO4 tetrahedra. The three dimensional framework includes elliptically shaped cavities approximately 12 Å in diameter called super cages. The Y-type zeolites with high (1.5-3.0) Si/Al ratios, 300 to 800 m2/g surface areas, are preferred given the thermal stability and the high catalytic activity. See C. V., McDaniel, P. K., Maher, “Zeolite stability and ultra stable zeolites”, Zeolite Chemistry and Catalysis, vol 4, pg. 225, 1984?]
Only a few studies of methane reforming have been conducted using nickel supported on zeolites see M., Iwamoto, T., Hasuwa, H., Furukawa, S., Kagawa, “Water Gas Shift Reaction Catalyzed by Metal Ion-exchanged Zeolites”, Journal of Catalysis, vol79, pg. 291, 1983 and B., Gustafson, J., Lunsford, “The Catalytic Reaction of CO and H2O over Ruthenium in a Y-Type Zeolite”, Journal of Catalysis, vol78, pg. 393, 1982. [16, 17].
These studies suggest that higher activity can be attained using zeolitic supports. In addition to higher activity, zeolitic supports have the potential to deliver very high metal dispersion that is stable combined with a low potential for support metal interaction.
There are many patents on catalysts that describe various catalyst structures for example U.S. Pat. No. 4,280,820 issued Jul. 28, 1981 describes a catalyst for use in the production of methane producing gases. This catalyst is formed by coprecipitation of Nickel Ni and alumina with in its unreduced precursor with a 12 to 120 Angstrom pores (Å) and has at least 55% of the pore volume in the 12 to 30 Å range and wherein the pore volume formed by pores with a radius of 10 to 50 Å is at least 80% of the total pore volume U.S. Pat. Nos. 4,990,481 issued Feb. 5, 1991 and 5,100,857 issued Mar. 31, 1992 to Sato et al each describes a catalyst formed by immersing the alumina particles in a Ni containing solution, drying and then calcining to produce a catalyst where the alumina has a pore size in the order of about 1000 Å to 5000 Å. It will be noted that these patents do not describe the size of the Ni crystallites.
EPO patent 114704 describes the formation of catalyst for hydrogenation reactions wherein a Ni catalyst on a suitable carrier is formed in a multi step process. The crystallite size of the Ni/Ni compound used is less than 10 nanometers.
WO 9849097 A1 of Hershkowitz published Nov. 5, 1998 describes a fluidized bed process and apparatus for producing synthesis gas discusses the use of catalyst with crystallites supported in the surface of 30 to 150 micron particles in concentrations ranging from 0.1 to 90% Ni based on the total weight of the mixture. This patent is particularly concerned with “the importance of Nickel loadings below 5%” to prevent the 30 to 150 micron “particle agglomeration” in the fluidized bed.